A typical coffee brew machine comprises a base member with a heater element used to support a glass coffee pot and a coffee filter holder attached to the base in the position above the coffee pot. The coffee filter holder is typically frusto-conical in shape with one or more central apertures through the bottom wall and is designed to receive a disposable coffee filter. The coffee filter is normally fabricated from porous paper and is also frusto-conical in shape so as to be received within the coffee filter holder. In use, the coffee filter will be placed in the coffee filter holder and a measured amount of roast and ground coffee is placed in the bottom portion of the coffee filter. A measured quantity of hot water is then directed into the interior of the coffee filter onto the ground coffee. As the water passes through, the coffee expands and floats up in the filter increasing the coffee/water contact area. The water will then percolate through the ground coffee and flow through the bottom and lower side portions of the porous coffee filter and through the coffee filter holder apertures down into the coffee pot.
One disadvantage with the aforementioned system is that the ground coffee must be individually measured into the coffee filter each time a pot of coffee is to be brewed. This is time consuming and may result in too much or too little coffee being placed in the filter. If the amount of coffee placed in the filter varies to any significant extent, then the brew strength of the resultant coffee will also vary. Another disadvantage is that separate receptacles must be provided for the individual coffee filters and the ground coffee. Lastly, when measuring the coffee into the coffee filter or disposing of a used filter, the coffee is often spilled onto the counter area or the floor resulting in waste of coffee and a waste of time in cleaning up.
Coffee manufacturers have substantially eliminated the pot-to-pot brew strength inconsistencies arising from poor measurement of coffee by the operator by providing unitized pouches, each containing a predetermined volume of roast and ground coffee suitable for brewing a single pot of coffee of reasonably consistent strength from one pot to the next. However, these unitized pouches add to cost and disposal problems due to the need for additional packaging equipment and material. In addition, they do not eliminate the messiness problems normally associated with bulk coffee/paper filter systems, since loose grounds and filters must still be disposed of.
Recently, coffee filter packs have been designed in an attempt to overcome some disadvantages from this method. Most of these coffee filter packs are made with heat sealable filter paper or from non-woven polyester, polypropylene, polyethylene or a combination thereof. These materials are typically more expensive than conventional filter paper, which is typically comprised almost entirely of wood fiber. Moreover, these filter packs are usually circular or square in shape and simply cover the bottom wall of the coffee filter holder. One example of such a filter pack is disclosed in U.S. Pat. No. 5,012,629 issued to Rehman on May 7, 1991. These filter packs are often improperly positioned in the coffee filter holder resulting in inconsistent brew strength from pot-to-pot, since their shape and materials of construction allow water to escape around the sides and through the coffee filter pack without sufficient exposure to all of the coffee contacted in the brew chamber of the filter pack. This results in poor coffee extraction. Furthermore, the coffee will often migrate to one side of the filter pack so that much of the water which does pass through the brew chamber of the filter pack does not contact any coffee. As a result, these filter packs produce brewed coffee with a relatively low level of extracted flavor solids as well as an inconsistent brew strength from pot-to-pot.
U.K. Patent Application GB 2,183,459 discloses yet another coffee filter pack having a pre-measured amount of ground coffee within a receptacle region or brew chamber. The receptacle region is defined by a pair of frusto-conical layers of porous filter paper mutually adhered to one another to form a substantially vertically extending sidewall. However, since the sidewall is constructed of initially porous paper material and there is no teaching of any need to render the sidewall substantially impervious to water to force all of the incoming water through the receptacle containing the ground coffee, it is believed that the filter pack disclosed in U.K. Patent Application GB 2,183,459 would not deliver any improvement in pot-to-pot brew strength consistency over the structure disclosed by Rehman.
Still other workers in the prior art have made a multi-component coffee filter pack having a frusto conical shaped side wall comprised of a rigid plastic material while the bottom portion of the pack comprises a coffee containing pouch which is made of porous material. The impermeable plastic side walls of the latter filter packs prevent water from escaping through the side walls and around the coffee containing porous pouch, thereby increasing at least the potential for coffee/water contact. Examples of devices using this concept are shown in U.K. Patent Application 2,156,662 and U.K. Patent 1,427,375. However, coffee filter packs of the latter type require careful and consistent placement on the coffee maker due to their rigid side walls and are generally quite expensive relative to the bulk coffee/filter paper systems they are intended to replace. Furthermore, some of these filter packs require that a new and expensive filter holder be attached to the coffee maker to permit their use.
Experience to date has been that filter packs of the prior art do much to overcome the messiness of the bulk coffee/filter paper systems they have replaced. Unfortunately, they have typically exhibited lower extraction efficiencies than the bulk coffee/filter paper systems. In addition they have typically introduced much worse pot-to-pot brew strength variation than bulk coffee systems using premeasured unitized pouches of roast and ground coffee in conjunction with paper filters. It is believed that these shortcomings of prior art coffee filter packs are due to a failure of prior art filter pack workers to recognize the importance of meeting certain previously undefined brewing parameters, which have for the first time been identified by applicants. For example, none of the foregoing references teach the importance of controlling the flow rates of liquids into and out of the brew chamber. By way of contrast, Applicant has learned that in order to minimize brew time, maximize flavor solids extraction and make a good pot of coffee, a substantial portion of the hot water directed into the filter pack must contact the coffee in the brew chamber after a substantially steady state brewing condition has been established within the brew chamber, i.e., after the brew chamber has been completely flooded with the incoming hot water so that the chamber expands to its maximum volume and allows substantially all of the coffee contained therein to loosely float within the chamber. Applicant has further learned that this is preferably done by providing a substantially water impermeable side wall having a height which is sufficient to retain at least enough water to permit complete immersion of the brew chamber when the brew chamber is in its fully expanded condition in combination with inlet and discharge flow rates into and out of the brew chamber that will cause the water to build up and puddle the coffee inside the brew chamber. If the water is not allowed to build up inside the brew chamber, as is typically the case with prior art filter packs, or if the coffee contained in the brew chamber of a prior art filter pack has shifted to one side of the brew chamber when the prior art filter pack is placed in the filter holder, the failure to properly control the inlet and outlet flow rates and the failure to provide a substantially water impermeable side wall having a height which is sufficient to retain at least enough water to completely immerse the brew chamber when the brew chamber is in its fully expanded condition will allow much of the water to flow directly through the brew chamber of the prior art filter pack without ever contacting any of the coffee.
In addition, applicants have learned that the brew chamber must be large enough to allow the roast and ground coffee room to expand and float while water is building up in the brew chamber in order to achieve sufficient coffee/water contact, i.e., to achieve a steady state brewing condition. This helps to prevent channeling of the water through the filter pack without sufficient coffee/water contact. Minimizing channeling is important, since channeling of the hot water directly through the brew chamber without sufficient coffee contact results in poor and inconsistent coffee flavor solids extraction.
It is therefore an object of the present invention to provide a coffee filter pack which overcomes many of the problems associated with the prior art brewing systems which employ bulk coffee and discrete paper filters, which approximates the extraction efficiency of systems employing bulk coffee and discrete paper filters, which provides reasonably consistent pot-to-pot brew strength without the need for premeasured unitized pouches of roast and ground coffee and which avoids the pot-to-pot brew strength inconsistency typically associated with prior art filter packs.
It is another object of the present invention to provide such a coffee filter pack which is relatively insensitive to operator placement within the filter holder of the coffee machine, which includes a substantially impermeable vertically oriented, conformable side wall, which is made almost entirely of relatively inexpensive flexible material, such as ordinary filter paper, and which can be used with a wide range of existing coffee filter holders without any need to modify them.